Electron Transport through Early Exponential‐Phase Anode‐Grown Geobacter sulfurreducens Biofilms

Abstract

Geobacter sulfurreducens biofilms were grown to early exponential phase (i.e. the point at which the catalytic current first begins to increase) on interdigitated microelectrode arrays (IDAs), resulting in the formation of sparse cell clusters surrounded by extracellular polymeric substance (EPS). Continuous domains of EPS (defined here to include extracellular materials including filaments), but not cell clusters, were observed to bridge the gaps between adjacent electrode bands. Electrochemical gate measurements revealed electrical continuity between adjacent IDA electrode bands, indicating that extracellular electron transport (EET) occurs through the EPS. The dependency of the source‐drain current on the gate potential is peak shaped, which is consistent with EPS acting as a redox conductor. The gate potential at which the maximum source‐drain current occurs is approximately 0.13 V more positive than that for stationary‐phase biofilms, indicating that redox cofactors involved in EET at the early exponential phase are different to those at the stationary phase.

Rapid and Quantitative Assessment of Redox Conduction Across Electroactive Biofilms by using Double Potential Step Chronoamperometry

“…Synthetic redox polymers had long been thought to be the only electron‐conducting hydrated matrixes allowing both facile mass transfer of dissolved reactants and products as well as rapid transport of electrons across their volume . Although the analogy of the charge transfer across anodic EAB and redox polymers has increasingly been highlighted, no quantitative comparison has been done in terms of charge transport parameters. Here we see that the products (C T × D app 1/2 ) recorded for hydrated redox polymers are comparable to those of EABs, but typically varies to a larger extent over 3 orders of magnitude at 10 −(9±1) mol cm −2 s −1/2 depending on their nature (backbone, chemistry and concentration of redox centers, extent of cross‐linking and electrolyte parameters) .…”

“…These electroactive biofilms (EABs) can release an excess of electrons generated by their metabolism to either solid minerals or inert electrodes as final electron acceptors, in the latter case generating electrical current. For this, EABs perform electron transfer (ET) across their matrices over tens of μm, a distance largely exceeding the typical dimensions of a single bacterium (∼1 μm) . This ability to perform long range ET has mostly been observed and studied in either of two model microorganisms, Shewanella oneidensis MR‐1 and especially Geobacter sulfurreducens , and in mixed culture EABs largely dominated by Geobacter spp…”

Enrichment of a High-Current Density Denitrifying Microbial Biocathode

“…13 Only recently has an organism been identified (Mariprofundus ferrooxydans) that can grow on a cathode without such manipulation from pure culture, 13 potentially providing a model system for study analogous to Geobacter sulfurreducens for microbial bioanodes. [14][15][16][17][18][19][20] In this study, we describe formation and preliminary characterization of a relatively high current density denitrifying microbial biocathode that operates at relatively high potential. Motivation for this research is energy efficient treatment of wastewater using microbial fuel cells (MFCs).…”

On the electron transfer through Geobacter sulfurreducens PilA protein

“…Moreover, the subsequent demonstration that filaments of S. oneidensis MR1 appear to be outer membrane and periplasmic extensions containing heme proteins further supports a noncoherent mechanism . In addition, analysis of electrochemical gate measurements performed on G. sulfurreducens biofilms under physiological relevant conditions based on a non coherent model also showed strong correlation between theory and experiments …”